The present invention relates to a tape rolling up device for rolling up a tape drawn out from a tape reel in a package strapping machine.
The package strapping machine draws a thermoplastic tape from the reel, and winds it around a package. The strap is tightened, and both ends of the tape are heated and pressed in order to weld them together. Package strapping machines have been widely used for packaging various kinds of articles.
A general construction of the package strapping machine is shown in FIG. 1. A base 1 is supported by a table, carrying a package A to be strapped thereon, so as to be laterally movable. A first clamp 2, a pressing means 3 and a second clamp 4 are disposed side by side immediately below the base 1. They are raised and lowered by a group of cams 6 on a cam shaft 5, driven by means of a motor M1. A tape-cutting mechanism 17 is disposed between an upper end of the first clamp 2 and an upper end of the pressing means 3. A heater (not shown) is advanced into and retreated out of a space between the base 1 and the pressing means 3.
A thermoplastic tape B is drawn out from a reel 7 onto the table from a space between a pair of tape delivery and tightening rolls 8, 9, that is, an upper tape delivery and tightening roll 8 and a lower tape delivery and tightening roll 9. The tape feeds through a tape guide 10 and a guide groove 11 of the first clamp 2, loops around the package on the table, and a leading end of the tape is then inserted beneath a lower surface of the base 1. Upon the pushing of a switch (not shown) by the leading end of the tape B, a motor M1 is started to begin the tightening and welding operation.
Of the above described tape delivery and tightening rolls 8, 9, the upper roll 8 is driven forwardly and reversely by means of a motor M2, while the lower roll 9 is pulled up by means of a spring 12, pressing it against the upper roll 8, and this pressing force serves as a tape delivery force.
In addition, the lower roll 9 is pushed up by means of a cam 13 mounted on the cam shaft 5 through a rotor 14 and a spring 15. During a tape tightening process a tape holding force is thus enhanced, whereby the tape can be tightened without slipping, to tightly tie the package A being strapped.
However, with the above described package strapping machine, when the tape B is tightened by means of the tape delivery and tightening rolls 8, 9, the tape B becomes loose in the area between the rolls 8, 9 and the reel 7. If this loosened portion of the tape is not taken up, the tape can become tangled.
By connecting an inner end of a spiral spring to the tape reel 7, tightening the spiral spring to accumulate a spring force when the tape is drawn out, and rotating the reel by the accumulated spring force when the tape is tightened, a simple method of taking up the loosened portion of the tape is achieved.
In order to roll up an excessively long tape by means of a spiral spring, a spiral spring which is comparatively rigid and has a large number of turns would be required.
However, a problem occurs in a situation where the torque of the motor M2 driving the tape delivery and tightening rolls 8, 9 is relatively small, as in a small-sized semiautomatic bench package strapping machine. Such a machine is used for packaging weak and small articles such as cake boxes or lunch boxes. If a force of the spiral spring is relatively large, the torque of the motor M2 may be less than the force of the spiral spring, preventing the delivery of the tape.